Yeah I think the biggest loss is Amy & the Halo/Infamous guy. Infamous SS's combat is SO MUCH better than the previous entries and it's just incredibly fun to play and traverse around. This is what Jamie brought to the game with his "30 seconds of fun" mindset. He was a great win for Sucker Punch and helped them make their best game ever and the first real "must-have" next-gen game that delivers on every front (combat, gameplay, story, graphics).
And of course Amy writes good characters, worlds and game concepts. From Soul Reaver to Uncharted. So her departure is a shame for ND, though they still have lots of other talent. Justin is neither good nor bad, UC3 was a bit weak, and when Amy left it made sense he'd be looking to get out too. The question is who will replace them as the new directors at ND? With The Last of Us guys working on The Last of Us 2 & The Last of Us movie, if ND wants two alternating franchises they'll need to promote someone to head up Uncharted or TLoU2 while Niel and co do the other one.
Stig is deserved. GoW3 wasn't even particularly good, it played decent and looked great, but the story was awful and may have killed the franchise going by Ascension sales. The fact his original IP where he couldn't just build off someone else's talent was terrible and wasted Sony a ton of money is not a big surprise and Sony should've canned his IP years ago for sure.
Same with the Evo guy. Evolution studios aren't even that great (they're no Psygnosis/Liverpool or Bizarre Creations; Motorstorm had one good game with Pacific Rift and the series was also a looker that played janky [awful rubberband AI in SP]). He screwed up getting Sony's launch game out and they kicked him. Maybe they can put someone from ex-Liverpool or ex-Bizarre in charge to make sure it ends up good when it finally comes out.
Guerrilla put out a terrible Killzone game (again). It makes sense to downsize a bit while they try a new IP since Killzone isn't getting them anywhere. They've got great art designers, but boy do they need better gameplay designers, directors and writers.
Hope The Order turns out well or I can see Ready at Dawn going back to low budget portable games or even worse getting shut down in the future.
Sony Japan studios, Team Ico, and Gran Turismo team are all fucking up a lot for years, so hopefully we'll start seeing some results from the guy who went over to shake things up a couple of years ago in the next few years and those guys can get back on track. Where the hell is the PS4 Hot Shots Golf?
For now what Sony seems to be doing what is in their best interest and is just being super Indie friendly and getting as much quality software on their machines as fast and often as possible. That will hold the system together while all these studios get back on track.
/Sony software in a nutshell